Stimulation Circuitry in an Implantable Stimulator Device for Providing a Tissue Voltage as Useful During Neural Response Sensing

Abstract

Stimulator circuitry useable in a stimulator device is disclosed. The circuitry includes biasing circuitry that can be used to generate a voltage to allow any one or more electrode on the device (including the case electrode and lead-based electrodes) to provide a common mode voltage (Vcm) to the tissue. Providing a stable Vcm to the tissue is particularly useful when sensing neural responses to the stimulation that the device provides. Switches are provided to couple each of the electrode nodes to one or more buses. This allows any of the electrodes to be selected to provide bipolar or monopolar stimulation, or to act to provide Vcm to the tissue during relevant pulses phases, including during passive charge recovery.

What is claimed is: 
     
         1 . A stimulator device configured to provide stimulation with a first phase and a second phase, comprising:
 a plurality of electrode nodes, wherein each of the electrode nodes is coupleable to a different electrode configured to contact a patient's tissue;   driver circuitry configurable to drive at least two of the electrode nodes during the first phase to provide a current through the tissue;   a first bus configured to receive a bias voltage from biasing circuitry;   a plurality of first switches, wherein each of the first switches is connected between a different one of the electrode nodes and the first bus;   a second bus;   a plurality of second switches, wherein each of the second switches is connected between a different one of the electrode nodes and the second bus;   a third switch connected between the first bus and the second bus.   
     
     
         2 . The stimulator device of  claim 1 , further comprising control circuitry, wherein the control circuitry is configured during the second phase to
 close the second switches connected to the at least two electrode nodes to recover charge stored in current paths of the at least two electrode nodes, and   issue a control signal to either open or close the third switch.   
     
     
         3 . The stimulator device of  claim 2 , further comprising a plurality of DC-blocking capacitors, wherein each of the DC-blocking capacitors is connected in series between one of the electrode nodes and a different one of the electrodes. 
     
     
         4 . The stimulator device of  claim 3 , further comprising a resistor in parallel across only one of the DC-blocking capacitors. 
     
     
         5 . The stimulator device of  claim 2 , wherein if the control circuitry issues the control signal to open the third switch, the control circuitry is further configured during the second phase to close at least one of the first switches to provide a common mode voltage to the tissue. 
     
     
         6 . The stimulator device of  claim 5 , wherein the second bus is not biased by circuitry during the second phase when the third switch is opened. 
     
     
         7 . The stimulator device of  claim 6 , wherein the stimulation further comprises a third phase, wherein the control circuitry is further configured to close the at least one of the first switches during the first phase, during the third phase, or during both the first phase and the third phase, to provide the common mode voltage to the tissue. 
     
     
         8 . The stimulator device of  claim 7 , wherein the third phase comprises a quite phase when the driver circuitry is not active. 
     
     
         9 . The stimulator device of  claim 5 , further comprising a case implantable in the tissue and comprising a conductive portion, wherein one of the electrodes comprises the conductive portion operating as a case electrode. 
     
     
         10 . The stimulator device of  claim 9 , further comprising at least one lead, wherein at least some of the electrodes are on the at least one lead operating as lead-based electrodes. 
     
     
         11 . The stimulator device of  claim 10 , wherein the stimulation is monopolar during the first phase to provide the current between the case electrode and at least one of the lead-based electrodes, wherein the common mode voltage is provided to the tissue at one or more of the lead-based electrodes. 
     
     
         12 . The stimulator device of  claim 10 , wherein the common mode voltage is provided to the tissue at the case electrode. 
     
     
         13 . The stimulator device of  claim 2 , wherein if the control circuitry issues the control signal to close the third switch, the control circuitry is further configured during the second phase to open all of the first switches to prevent a common mode voltage from forming in the tissue during the second phase. 
     
     
         14 . The stimulator device of  claim 13 , wherein the stimulation further comprises a third phase, wherein the third phase comprises a quite phase when the driver circuitry is not active. 
     
     
         15 . The stimulator device of  claim 14 , wherein the control circuitry is further configured to
 close at least one of the first switches during the first phase, during the third phase, or during both the first phase and the third phase, to provide the common mode voltage to the tissue; or   open all of the first switches during the first phase, the third phase, or during both the first phase and the third phase; or open the second switches during the first phase, during the third phase, or during both the first phase and the third phase.   
     
     
         16 . The stimulator device of  claim 1 , wherein the stimulation comprises a plurality of phases during the first phase. 
     
     
         17 . The stimulator device of  claim 1 , wherein the stimulation is monophasic during the first phase. 
     
     
         18 . The stimulator device of  claim 1 , wherein the driver circuitry is powered by a compliance voltage. 
     
     
         19 . The stimulator device of  claim 18 , wherein the bias voltage comprises approximately one half of the compliance voltage. 
     
     
         20 . The stimulator circuitry of  claim 1 , further comprising neural response detection circuitry coupled to the electrode nodes, wherein the neural response detection circuitry is configured to measure a neural response to the current at one or more of the electrode nodes.